JP2016197606A - Nonaqueous electrolytic solution and lithium secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide nonaqueous electrolytic solution with which corrosion of aluminum used as a positive electrode current collector is suppressed and aging deterioration of battery performance is difficult to occur, and a lithium secondary battery using the same.SOLUTION: Nonaqueous electrolytic solution contains an imide-based compound represented by the following general formula (1), a borate compound represented by the following general formula (2) and/or a boron compound represented by the following general formula (3), and carbonate-based solvent: (XSO)(X'SO)NLi(1), M([BY])(2), and BY(3) (in the formula (1), X and X' represent F, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group having 1 to 6 carbon atoms, and at least one of X and X' is F, and in the formulas (2) and (3), Mrepresents organic or inorganic cation of monovalent to trivalent, and Yand Yare the same or different and represent hydrocarbon groups having 1 to 10 carbon atoms in the main chain which may have H, halogen atom, cyano group, halogen and represent -ZR, and n represents an integer of 1 to 3, respectively).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-aqueous electrolyte, and more particularly to a non-aqueous electrolyte provided in a lithium secondary battery and a lithium secondary battery using the same.

  In recent years, since lithium secondary batteries have high energy density, they have been used as power sources for mobile communication devices, power sources for portable information terminals, etc., and the market has grown rapidly with the spread of these terminals. Various researches have been made for the purpose of ensuring safety, improving cycle characteristics and energy density, and improving high-temperature storage characteristics.

For example, Patent Document 1 discloses a nonaqueous electrolytic solution containing lithium bisfluorosulfonylimide (LiN (SO ₂ F) ₂ ) having high thermal stability and a lactone having a high boiling point, and such a combination is disclosed. Discloses a technique for minimizing swelling of a non-aqueous electrolyte secondary battery during high-temperature exposure or storage. Non-Patent Document 1 discloses lithium bis (perfluoromethylsulfonyl) imide (LiN (SO ₂ CF ₃ ) ₂ ) and lithium bis (perfluoroethylsulfonyl) imide (LiN (SO ₂ C ₂ F ₅ ) ₂ ). A technique for suppressing corrosion of aluminum used as a positive electrode current collector by using LiPF ₆ in the case where is used as an electrolyte is disclosed.

JP 2004-165151 A

Xianming Wang et al., “Electrochimica Acta”, 45, 2000, p. 2677-2684

As described in Patent Document 1 and Non-Patent Document 1, imide compounds such as LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , and LiN (SO ₂ C ₂ F ₅ ) ₂ are used. Although there is a merit that ion conductivity or thermal stability is higher than conventional electrolytes such as LiPF ₆ , a lithium secondary battery using a non-aqueous electrolyte containing the imide compound is a high voltage of 4 V or more. When operated by voltage, there is a problem that aluminum used as a positive electrode current collector is corroded. In particular, when LiN (SO ₂ F) ₂ is used as the main electrolyte (for example, about 50% by mass or more of the total amount of the electrolyte), corrosion of the positive electrode current collector is sufficiently suppressed even when LiPF ₆ is used in combination. There was a problem that I couldn't.

  The present invention has been made paying attention to the circumstances as described above, and its purpose is non-aqueous electrolysis in which corrosion of aluminum used as a positive electrode current collector is suppressed and deterioration of battery performance with time is unlikely to occur. The object is to provide a liquid and a lithium secondary battery including the same.

The non-aqueous electrolyte solution of the present invention that has achieved the above object is an imide-based compound represented by the following general formula (1):
(XSO ₂ ) (X′SO ₂ ) N ⁻ Li ⁺ (1)
(X and X ′ represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group having 1 to 6 carbon atoms, and at least one of X and X ′ is a fluorine atom.)
A borate compound represented by the following general formula (2) and / or a borate compound represented by the following general formula (3);
_{^{M n + [(BY 1 4}} ) -] n (2)
BY ² ₃ (3)
(In the formulas (2) and (3), M ^{n +} represents a monovalent, divalent, or trivalent organic or inorganic cation, and Y ¹ and Y ² are the same or different and represent a hydrogen atom, a halogen atom, or a cyano group. Represents a hydrocarbon group having 1 to 10 carbon atoms in the main chain optionally having halogen, -Z ¹ R ¹⁴ , wherein R ¹⁴ is a hydrogen atom, a halogen atom, or a main chain having 1 to 4 atoms; 10 represents an organic substituent, Z ¹ represents O or S, and n represents an integer of 1 to 3.)
It is characterized by including a carbonate-based solvent.

The nonaqueous electrolytic solution of the present invention preferably contains a borate compound represented by the above general formula (2). In the borate compound represented by the above general formula (2), Y ¹ is fluorine. An atom or a fluoroalkyl group is preferred. The borate compound represented by the general formula (2) preferably contains a boron tetrafluoride anion (BF ₄ ⁻ ).

The non-aqueous electrolyte of the present invention preferably further contains an electrolyte represented by the following general formula (4).
M′PF _a (C _m F _{2m + 1} ) _6-a (0 ≦ a ≦ 6, 1 ≦ m ≦ 2) (4)
(In formula (4), M ′ represents an alkali metal ion.)
As the imide compound represented by the general formula (1), lithium bis (fluorosulfonyl) imide is preferable. Moreover, it is a preferable embodiment of the present invention that the electrolyte represented by the above formula (4) is LiPF ₆ .

  The present invention also includes a lithium secondary battery using the non-aqueous electrolyte.

  According to the nonaqueous electrolytic solution of the present invention, corrosion of aluminum used as the positive electrode current collector can be suppressed. Therefore, it is expected that the lithium secondary battery provided with the non-aqueous electrolyte of the present invention is unlikely to deteriorate with time in battery performance.

It is a figure which shows the CV measurement result of Example 1. It is a figure which shows the CV measurement result of the comparative example 1.

1. Nonaqueous Electrolyte The nonaqueous electrolyte of the present invention includes an imide compound represented by the following general formula (1),
(XSO ₂ ) (X′SO ₂ ) N ⁻ Li ⁺ (1)
(In general formula (1), X and X ′ represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group having 1 to 6 carbon atoms, and at least one of X and X ′ is a fluorine atom. .)
A borate compound represented by the following general formula (2) and / or a boron compound represented by the following general formula (3);
_{^{M n + [(BY 1 4}} ) -] n (2)
BY ² ₃ (3)
(In the general formulas (2) and (3), M ^{n +} represents a monovalent, divalent, or trivalent organic or inorganic cation, and Y ¹ and Y ² are the same or different and represent a hydrogen atom, a halogen atom, cyano. Group, a hydrocarbon group having 1 to 10 carbon atoms in the main chain which may have a halogen, -Z ¹ R ¹⁴ , wherein R ¹⁴ is a hydrogen atom, a halogen atom, or a main chain having 1 atom. Represents an organic substituent of from 10 to 10, Z ¹ is O or S
N represents an integer of 1 to 3. )
It is characterized in that it contains a carbonate-based solvent.

As described in Non-Patent Document 1, the effect of inhibiting corrosion when lithium bis (perfluoroalkylsulfonyl) imide is used as an electrolyte is most prominent when LiPF ₆ is used among lithium salt compounds. For example, LiBF _{In order} to achieve a corrosion potential of 4.5V using ₄ , an addition amount more than three times that of LiPF ₆ is required. However, according to the study by the present inventors, LiPF ₆ is added in a non-aqueous electrolyte solution containing an imide compound represented by the general formula (1) (hereinafter referred to as imide compound (1)). However, it was difficult to obtain the same effect, and it was difficult to sufficiently suppress the corrosion of the aluminum current collector.

Therefore, the present inventor has repeatedly investigated the corrosion inhibition of an aluminum current collector (positive electrode current collector) in a lithium secondary battery provided with a nonaqueous electrolytic solution containing the imide compound (1) as an electrolyte. A non-aqueous electrolyte is a borate compound represented by the above general formula (2) (hereinafter referred to as a borate compound (2)) or a boron compound represented by the above general formula (3) (hereinafter referred to as boron). In the case of containing the compound (3)), it has been found that an excellent corrosion inhibitory effect of the aluminum current collector can be obtained as compared with LiPF ₆ .

The mechanism by which the corrosion of the aluminum current collector is more effectively suppressed when the borate compound (2) and / or the boron compound (3) is used is not understood in detail. The inventors speculate as follows. That is, the effect of inhibiting corrosion due to the use of LiPF ₆ is due to the formation of a passive film of AlF _{3 on} the surface of the aluminum current collector, whereas in the present invention, it is included in the non-aqueous electrolyte. In addition to the passive film of AlF ₃ derived from F atoms contained in the components, an AlBO ₃ film, which is a passive film derived from B atoms, is also generated, so that the passive film is sufficient for inhibiting corrosion of the aluminum current collector. Is generated quickly, and the combined effect of the fluorine-based passivated film and the boron-based passivated film is considered to provide a better corrosion inhibiting effect.

Hereinafter, the nonaqueous electrolytic solution of the present invention will be described.
1-1. Borate compound and / or boron compound 1-1-1. Borate compound according to the borate compound present invention (2) has the general formula ^{(2); M n + [} (BY 1 4) -] is represented by _n. Here, in the general formula (2), M ^{n +} represents a monovalent, divalent, or trivalent organic or inorganic cation, and Y ¹ is the same or different and has a hydrogen atom, a halogen atom, a cyano group, or a halogen. Represents a hydrocarbon group having 1 to 10 carbon atoms in the main chain, -Z ¹ R ¹⁴ , where R ¹⁴ is a hydrogen atom, a halogen atom, or an organic substitution having 1 to 10 atoms in the main chain Z ¹ represents O or S
N represents an integer of 1 to 3. In the general formula (2), two or more Y ¹ may be bonded to form a ring containing B.

In the general formula (2), as the organic cation represented by M ^{n +} , the general formula (5): L ⁺ -R _S (wherein L represents C, Si, N, P, S or O, R is the same or different organic group, and may be bonded to each other, s represents the number of R bonded to L, and is 2, 3 or 4. Note that s is the valence of the element L and An onium cation represented by the number of double bonds directly bonded to L is preferable.

The “organic group” represented by R means a group having at least one hydrogen atom, fluorine atom, or carbon atom. The “group having at least one carbon atom” only needs to have at least one carbon atom, and may have another atom such as a halogen atom or a hetero atom, a substituent, or the like. Good. Examples of the substituent include amino group, imino group, amide group, ether bond group, thioether bond group, ester group, hydroxyl group, alkoxy group, carboxyl group, carbamoyl group, cyano group, disulfide group, nitro group. Group, nitroso group, sulfonyl group and the like.

  Examples of the onium cation represented by the general formula (5) include those represented by the following general formula.

(R in the formula is the same as in the general formula (5))

  Among the six onium cations represented by the above general formula, those in which L in the general formula (5) is N, P, S or O are more preferable, and onium cations in which L is N are more preferable. The said onium cation may be used independently and may use 2 or more types together. Specifically, examples of the onium cation in which L is N, P, S, or O include those represented by the following general formulas (6) to (8).

  General formula (6):

At least one of 15 types of heterocyclic onium cations represented by the formula:

Examples of the organic groups R ^{1 to} R ⁸ include the same organic groups R exemplified in the general formula (5). More specifically, R ^{1 to} R ⁸ are a hydrogen atom, a fluorine atom, or an organic group, and examples of the organic group include a straight chain, a branched chain, or a ring (provided that R ^{1 to} R ⁸ are bonded to each other to form a ring). Are preferably a hydrocarbon group having 1 to 18 carbon atoms or a fluorine group, and more preferably a hydrocarbon group having 1 to 8 carbon atoms or a fluorine group. Moreover, the organic group may contain the substituent illustrated about the said General formula (5), hetero atoms, such as N, O, and S, and a halogen atom.

  General formula (7):

(In the formula, R ^{1 to} R ¹² are the same as R ^{1 to} R ^{8 in} formula (6)).
At least one of nine types of saturated ring onium cations represented by the formula:

  General formula (8):

(In the formula, R ^{1 to} R ⁴ are the same as R ^{1 to} R ^{8 in} the general formula (6)).
A chain onium cation represented by

For example, the chain onium cation represented by the general formula (8) includes tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, tetraheptylammonium, tetrahexylammonium, tetraoctylammonium, triethylmethylammonium, methoxy Ethyl diethylmethylammonium, trimethylphenylammonium, benzyltrimethylammonium, benzyltriethylammonium, benzyltributylammonium, dimethyldistearylammonium, diallyldimethylammonium, 2-methoxyethoxymethyltrimethylammonium and tetrakis (pentafluoroethyl) ammonium, N-methoxytrimethyl Ammonium, N-ethoxylate Methyl ammonium, quaternary ammonium such as N- propoxymethyl trimethylammonium, trimethylammonium, triethylammonium,
Tertiary ammoniums such as tributylammonium, diethylmethylammonium, dimethylethylammonium, dibutylmethylammonium, secondary ammoniums such as dimethylammonium, diethylammonium, dibutylammonium, methylammonium, ethylammonium, butylammonium, hexylammonium, Examples include primary ammoniums such as octylammonium, and ammonium compounds represented by NH ₄ .

  Among the onium cations of the above general formulas (6) to (8), an onium cation containing a nitrogen atom is more preferable, and a more preferable one is the following general formula:

(Wherein, R ¹ to R ¹² are the same as R ¹ to R ⁸ of general formula (6).)
And at least one of six kinds of onium cations represented by the formula:

  Among the six kinds of onium cations, chain quaternary ammonium such as tetraethylammonium, tetrabutylammonium and triethylmethylammonium, chained tertiary ammonium such as triethylammonium, tributylammonium, dibutylmethylammonium and dimethylethylammonium, Pyrrolidiniums such as 1-ethyl-3-methylimidazolium and imidazolium such as 1,2,3-trimethylimidazolium, N, N-dimethylpyrrolidinium and N-ethyl-N-methylpyrrolidinium are readily available. It is more preferable because it exists. More preferred are quaternary ammonium and imidazolium.

On the other hand, the inorganic ^{cation, H +, Li +, Na} +, K +, 1 monovalent inorganic cations M ¹⁺ of Cs ^{+, etc.; Mg 2+, Ca 2+, Zn} 2+, Pd 2+, Sn 2 ^{+, Hg 2+, Rh 2+,} Cu 2+, Be 2+, Sr 2+, Ba 2+, divalent Pb ²⁺ and inorganic cations M ^2+; and trivalent Ga ³⁺ etc. Inorganic cation M ³⁺ may be mentioned. Among these, Li ⁺ , Na ⁺ , Mg ²⁺ and Ca ²⁺ are preferable because they have a small ionic radius and can be easily used for power storage devices and the like, and a more preferable inorganic cation M ^{n +} is Li ⁺ .

The general formula (2) an anion represented (BY ¹ ₄₎ ^- in the case Y ¹ is a halogen atom, the halogen atom, F, Cl, include Br or I. Of the halogen atoms, F (fluorine) is preferred.

When Y ¹ is a hydrocarbon group having 1 to 10 carbon atoms in the main chain which may have a halogen, the hydrocarbon group may be a methyl group, an ethyl group, an n-propyl group, or iso-propyl. Group, n-butyl group, iso-butyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, octyl group, 2-ethylhexyl group and other alkyl groups having 1 to 10 carbon atoms; vinyl Group, propenyl group, isopropenyl group, allyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, 1,3-butadienyl group, 1-cyclohexenyl group, 2-cyclohexenyl group, 3-cyclohexenyl group Group, alkenyl group having 1 to 10 carbon atoms such as methylcyclohexenyl group, ethylcyclohexenyl group; ethynyl group, propargyl group, cyclohexylethynyl group, Eniruechiniru alkynyl group having 1 to 10 carbon atoms such group; a phenyl group, a benzyl group, a thienyl group, a pyridyl group, an aryl group or a hetero atom-containing aryl group having 6 to 10 carbon atoms such as an imidazolyl group; and the like.

  Examples of the halogenated hydrocarbon group having 1 to 10 carbon atoms in the main chain include those in which part or all of the hydrogen atoms of the hydrocarbon group are substituted with halogen (F, Cl, Br or I). For example, fluoromethyl group, difluoromethyl group, trifluoromethyl group, chloromethyl group, bromomethyl group, iodomethyl group, difluorochloromethyl group, fluorodichloromethyl group, fluoroethyl group, difluoroethyl group, trifluoroethyl group, tetrafluoro Ethyl group, perfluoroethyl group, fluorochloroethyl group, chloroethyl group, fluoropropyl group, perfluoropropyl group, fluorochloropropyl group, perfluorobutyl group, perfluorooctyl group, pentafluorocyclohexyl group, perfluorocyclohexyl group, Examples thereof include halogenated alkyl groups and halogenated aryl groups such as a pentafluorophenyl group, a perchlorophenyl group, a fluoromethylene group, a fluoroethylene group, and a fluorocyclohexene group.

The hydrocarbon group having 1 to 10 carbon atoms in the main chain which may have a halogen has a substituent (for example, an alkoxy group, an amino group, a cyano group, a carbonyl group, a sulfonyl group, etc.). Also good. Moreover, you may have a functional group containing hetero atoms, such as Si, B, O, N, and Al. Examples of the functional group containing a hetero atom include a cyano group, a trimethylsilyl group, a triethylsilyl group, a dimethoxyaluminum group, —CH ₂ CH ₂ B (CN) ₃ , —C ₃ H ₆ B
(CN) ₃ etc. are mentioned.

If the Y ¹ is -Z ¹ R ^14, examples of R ¹⁴ atoms in the main chain is 1-10 organic substituent, linear, branched, or cyclic, Of these, two or more structures may be included, and a substituent may be included. Two or more Y ¹ may be bonded to each other to form a cyclic structure. Furthermore, the organic substituent R ¹⁴ may contain an unsaturated bond. The number of atoms in the main chain of the organic substituent R ¹⁴ is as described above, but the number of carbons (including the substituent) contained in the organic substituent R ¹⁴ is preferably in the range of 1 to 20, more preferably. Is in the range of 1-10. The organic substituent R ¹⁴ may contain heteroatoms (O, N, S, Si, etc.) other than carbon and hydrogen, and halogen atoms (F, Cl, Br, etc.). There is no particular limitation. Therefore, for example, when at least one of Y ^{1 in} the general formula (2) is Z ¹ R ¹⁴ , the kind of atoms adjacent to Z ¹ is not particularly limited, and may be carbon, or
For example, it may be a heteroatom such as Si or Al. Further, the organic substituent R ¹⁴ may be composed only of atoms other than carbon.

Specific examples of the organic substituent R ¹⁴ include a saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, a cyanated hydrocarbon group, an alkoxylated and / or aryloxylated hydrocarbon group, and an alkanoyl group. An organic substituent, an organic substituent having an ester bond, a nitrogen-containing organic substituent, a group having a thioalkoxy structure, an organic substituent having a sulfinyl group, an organic substituent having a sulfonyl group, an organic substituent having a hetero atom,- CH ₂ CH ₂ OB (CN) ₃ , —C ₃ H ₆ OB (CN) ₃ ;

Specific examples of the borate compound (2) include HBF ₄ , KBF ₄ , KBBr ₄ , LiBF ₄ , NaBH _{4 and the} like, and NaB represented by the general formula of M ^{n +} B ⁻ (Z ¹ R ¹⁴ ) _4. (OH) ₄ , KB (O
Tetrahydroborates such as H) ₄ and LiB (OH) ₄ , LiB (CN) ₄ , LiB (O
Examples include cyano group-containing lithium salts such as CH ₃ ) (CN) ₃ and LiB (OC ₂ H ₅ ) (CN) ₃ , and compounds represented by the following general formula (2-1).

In general formula (2-1), Y ³ and Y ⁴ are the same or different and are a hydrogen atom, a halogen atom, a hydrocarbon group having 1 to 10 carbon atoms in the main chain which may have halogen, cyano Represents a group, —C (O) R ¹⁵ , —S (O) ₁ R ¹⁵ , —Z ² (R ¹⁵ ) ₂ or —Z ¹ R ¹⁵ , wherein R ¹⁵ represents a hydrogen atom, a halogen atom, or a main chain; Represents an organic substituent having 1 to 10 atoms, Z ² represents N or P, l
Represents an integer of ¹ to 2, m represents an integer of 1 to 3, p represents an integer of 0 to 10 (preferably 0 to 4, more preferably 0 to 2) (Z ¹ and n are general Same as in the case of formula (2)).

  As anions of the borate compound represented by the general formula (2-1), cyanooxalatoborate (p = 0), cyanomalonatoborate (p = 1), cyanosuccinateborate (p = 2), And cyanoglutaratoborate (p = 3), cyanoadipolatoborate (p = 4), and the like.

In the general formula (2-1), when Y ³ and Y ⁴ are halogen, examples of the halogen atom include F, Cl, Br, and I. Among these, F (fluorine) is preferable.

Examples of the hydrocarbon group having 1 to 10 carbon atoms in the main chain which may have a halogen represented by Y ³ and Y ⁴ include the same ones as Y ¹ .

In the above -C (O) R ¹⁵ , -S (O) ₁ R ¹⁵ , -Z ² (R ¹⁵ ) ₂ and -Z ¹ R ¹⁵ , R ¹⁵ is H, halogen or the number of atoms of the main chain. Represents 1-10 organic substituents. As the halogen atom, fluorine, chlorine, bromine, iodine or the like is preferable. Examples of the organic substituent having 1 to 10 atoms in the main chain are the same as those described above for R ¹⁴ . Further, even if contained in the organic substituent R ¹⁵ is a heteroatom or a halogen atom is not particularly limited in the number and position, for example, for Y ^3, Y ⁴ in the general formula (2-1), Y ³ , Y ⁴ is —Z ¹ R ¹⁵ , the type of atoms adjacent to Z ¹ is not particularly limited, and may be, for example, carbon, or a heteroatom such as Si or Al. The organic substituent R ¹⁵ may be composed only of atoms other than carbon.

When Y ³ and Y ⁴ are represented by —C (O) R ¹⁵ , R ¹⁵ is a saturated or unsaturated hydrocarbon group or halogenated hydrocarbon group, alkoxylated or aryloxylated hydrocarbon group, Or it is preferably a nitrogen-containing organic substituent, and R ¹⁵ is more preferably a methyl group, an ethyl group, a phenyl group, a trifluoromethyl group, or a pentafluorophenyl group. Therefore, the substituents Y ³ and Y ⁴ include acetyl group, propanoyl group, butanoyl group, pentanoyl group, hexanoyl group, heptanoyl group, octanoyl group, isobutanoyl group, trifluoroacetyl group, benzoyl group, pentafluorobenzoyl group, acryloyl Group, methacryloyl group, methyl oxalyl group (—COCOCH ₃ ), methyl malonyl group (—COCH ₂ COCH ₃₎
), Organic substituents including alkanoyl groups including linear, branched, cyclic or combinations thereof, such as methylsuccinyl group (—COCH ₂ CH ₂ COCH ₃ ), acetoxymethylcarbonyl group, acetoxyethylcarbonyl group, benzoyl Organic substituents having ester bonds including linear, branched, cyclic or combinations thereof, such as oxyethylcarbonyl group, methoxycarbonyl group, ethoxycarbonyl group, methoxyethyleneoxycarbonyl group; amide group, N-alkylamide And nitrogen-containing organic substituents including linear, branched, cyclic, or combinations thereof, such as a group and an N-phenylamide group.

When Y ³ and Y ⁴ are represented by —S (O) ₁ R ¹⁵ , R ¹⁵ is a halogen atom, or
A saturated or unsaturated hydrocarbon group or a halogenated hydrocarbon group is preferred, and a halogen or halogenated hydrocarbon group is more preferred. Specifically, as —S (O) ₁ R ¹⁵ , fluorosulfinyl group, chlorosulfinyl group, trifluoromethylsulfinyl group, pentafluoroethylsulfinyl group, phenylsulfinyl group, pentafluorophenylsulfinyl group, tolylsulfinyl group, etc. Sulfonyl groups (l = 1), fluorosulfonyl groups, chlorosulfonyl groups, trifluoromethylsulfonyl groups, pentafluoroethylsulfonyl groups, tolylsulfonyl groups, phenylsulfonyl groups, pentafluorophenylsulfonyl groups and the like (l = 2) ) Is more preferable.

When Y ³ and Y ⁴ are represented by —Z ² (R ¹⁵ ) ₂ , an amino group in which Z ² is N such as a dimethylamino group and an ethylmethylamino group; a diphenylphosphino group and a dicyclohexylphosphino group A phosphino group in which Z ² is P, and the like.

When Y ³ and Y ⁴ are represented by —Z ¹ R ¹⁵ , Z ¹ is O, and R ¹⁵ may have a halogenated hydrocarbon group having 1 to 20 carbon atoms (for example, A group that is a saturated hydrocarbon group or an unsaturated hydrocarbon group such as a methyl group, an ethyl group, a phenyl group, a pentafluorophenyl group, a trifluoromethyl group, or a pentafluoroethyl group; Z ¹ is O, and R ¹⁵ A group in which is an alkylsilyl group (eg, trimethylsilyl group, triethylsilyl group, etc.); Z ¹ is O;
R ¹⁵ is monovalent, linear, branched, cyclic or an alkanoyl group selected from combinations thereof (for example, acetyl group, trifluoroacetyl group, propanoyl group, butanoyl group, pentanoyl group, hexanoyl group, heptanoyl group) , octanoyl group, isopropanoyl alkanoyl group, isobutanoyl group, a benzoyl group, pentafluorobenzoyl group, an acryloyl group, a methacryloyl group, methyl oxalyl group, methylmalonyl group, group a Mechirusukushiniru group); a is Z ¹ O , R ¹⁵ is a sulfinyl group (e.g., fluoro-sulfinyl group, chloro sulfinyl group, trifluoromethyl sulfinyl group, tolyl-sulfinyl group, etc.), or a sulfonyl group (fluorosulfonyl group, chlorosulfonyl group, trifluoromethylsulfonyl group, Torirusuruhoni Group is a group); Z ¹ is an S, group R ¹⁵ is a hydrocarbon group having 1 to 20 carbon atoms that may have a halogen (e.g., methylthio group, trifluoromethylthio group and the like) And the like.

  More specific examples of the anion of the borate compound according to the present invention include those represented by the following formulas (2-1-1) to (2-1-14) (p is an integer of 0 to 2). However, 0 or 1 is preferable, and 0 is more preferable. Preferred anions are (2-1-1), (2-1-2), (2-1-3), (2-1-4), (2-1-7), (2-1-9) ) And (2-1-10).

Among the borate compounds (2) exemplified above, Y ¹ is preferably a compound containing fluorine, a fluoroalkyl group or a cyano group. Specifically, LiBF ₄ , LiB (CN) ₄ , LiB (OCH ₃ ) (CN) ₃ , LiB (OC ₂ H ₅ ) (CN) ₃ , general formula (2-1-1)
A lithium salt of a compound represented by the general formula (2-1-2) (particularly, p is 0 to 2) is preferable, and LiBF ₄ , the general formula (2-1-1), and the general formula (2-1-1). 2) (especially,
A lithium salt having p of 0 to 1) is more preferable, and LiBF ₄ containing a boron tetrafluoride anion is particularly preferable. A borate compound (2) may be used individually by 1 type, and may be used in combination of 2 or more type.

1-1-2. Boron Compound The boron compound (3) according to the present invention is a compound represented by the general formula (3); BY ² ₃ (
Y ² in the general formula (3) is the same as Y ¹ in the general formula (2)). The boron compound (3) may form a complex with other compounds.

Specific examples of the boron compound (3) include compounds represented by B (Z ¹ R ¹⁴ ) ₃ in addition to BH ₃ , BF ₃ , BCl ₃ , BBr ₃ , BI _{3 and the} like. Examples of the compound represented by B (Z ¹ R ¹⁴ ) ₃ include boric acid; B (OMe) ₃ , B (OEt) ₃ , B (Oi-Pr) ₃ , B (Ot-
Bu) ₃ (-t- represents “tert”; the same applies hereinafter), B (OPh) ₃ , B (OTMS) ₃ , B (O (C ₆ F ₅ )) ₃ , B (OCH (CF ₃ ) Boric acid esters such as ₂ ) ₃ , B (On-Bu) ₃ , (-n- represents "normal", the same shall apply hereinafter); B (SMe) ₃ , B (SEt) ₃ And boric acid thioesters such as B (S-i-Pr) ₃ , B (St-Bu) ₃ , and B (SPh) ₃ .

  Compounds that form complexes with the boron compound (3) include ethers such as diethyl ether, tripropyl ether, tributyl ether, tetrahydrofuran, ammonia, methylamine, ethylamine, butylamine, hexylamine, octylamine, dimethylamine, diethylamine, Examples thereof include amines such as dibutylamine, dihexylamine, dicyclohexylamine, trimethylamine, triethylamine, tributylamine, triphenylamine, guanidine, aniline, morpholine, pyrrolidine, and methylpyrrolidine.

Among the boron compounds (3) exemplified above, B (OMe) ₃ , B (OEt) ₃ and B (Oi-Pr) ₃ are preferable, and B (OMe) ₃ and B (OEt) ₃ are more preferable. More preferred is B (OMe) ₃ . A boron compound (3) may be used individually by 1 type, and may be used in combination of 2 or more type.

  The borate compound (2) and the boron compound (3) may be used in combination, or either one may be used alone, but the borate compound (2) (especially lithium is used). Use) is preferable because the lithium salt concentration of the non-aqueous electrolyte can be improved.

  The amount of the borate compound (2) and / or boron compound (3) used is the non-aqueous electrolyte solution according to the present invention (that is, the imide compound (1), the borate compound (2) and / or the boron compound. (3) The total amount of optional additives such as the solvent and the electrolyte (4) and additives described later) is preferably 0.05 to 30 parts by mass with respect to 100 parts by mass. More preferably, it is 0.1-20 mass parts, More preferably, it is 0.2-15 mass parts. If the amount of the borate compound (2) and / or boron compound (3) used is too small, the effect of preventing the corrosion of the positive electrode current collector may be insufficient. There is a risk that the viscosity will increase and the ionic conductivity will decrease.

1-2. Imide compound The non-aqueous electrolyte of the present invention is an imide compound represented by the general formula (1): (XSO ₂ ) (X′SO ₂ ) N ⁻ Li ⁺ (in the formula (1), X, X ′ Represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group having 1 to 6 carbon atoms, and at least one of X and X ′ is a fluorine atom.

In the imide compound (1) contained in the nonaqueous electrolytic solution according to the present invention, F atoms directly bonded to S atoms exist, and some F atoms are formed by applying a voltage to the nonaqueous electrolytic solution. Desorbed from the S atom. The desorbed F atoms react with Al (positive electrode current collector) to produce a passive film: AlF ₃ , but the corrosion reaction of Al proceeds more than the passive film formation reaction under normal use environment. Since this was faster, corrosion occurred in the positive electrode current collector, which was a problem.

However, by using the imide-based compound (1) in combination with the borate compound (2) and / or the boron compound (3), not only a passive film by AlF ₃ but also B atoms in the film. It is presumed that the inhibition of corrosion of the positive electrode current collector has become more effective because the composite passive film incorporated is generated.

  In the general formula (1), the alkyl group having 1 to 6 carbon atoms represented by X and X ′ may be linear, branched, cyclic, or a combination thereof. . A linear alkyl group is preferable, and examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, and a hexyl group.

The fluoroalkyl group may be linear, branched, cyclic, or a combination thereof, and some or all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms. Things. Specific examples of the fluoroalkyl group include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a fluoroethyl group, a difluoroethyl group, a trifluoroethyl group, a pentafluoroethyl group, a fluoropropyl group, a fluoropentyl group, and a fluorohexyl group. Groups and the like.
X and X ′ are preferably a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group.

  Preferred imide compounds (1) include lithium bis (fluorosulfonyl) imide, lithium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, lithium (fluorosulfonyl) (pentafluoroethylsulfonyl) imide, potassium bis (fluorosulfonylimide) ), Potassium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, sodium bis (fluorosulfonylimide), sodium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, and more preferably lithium bis (fluorosulfonyl) imide , Lithium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, lithium (fluorosulfonyl) (pentafluoroethylsulfonyl) imide, Preferred is lithium bis (fluorosulfonyl) imide. As the imide compound (1), a commercially available product may be used, or a compound synthesized by a conventionally known method may be used.

  The amount of the imide compound (1) used is preferably such that the concentration in the non-aqueous electrolyte of the present invention is 0.01 mol / L or more and 2 mol / L or less. More preferably, it is 0.02 mol / L-1.8 mol / L, More preferably, it is 0.05 mol / L-1.7 mol / L, More preferably, it is 0.08 mol / L-1.6 mol / L. And still more preferably 0.1 mol / L to 1.5 mol / L.

1-3. Carbonate Solvent The nonaqueous electrolytic solution of the present invention contains a carbonate solvent as a solvent for dissolving the imide compound (1), the borate compound (2) and / or the boron compound (3). A carbonate-based solvent is preferably used because it is difficult to decompose upon application of a voltage and is stable.

  Examples of the carbonate solvent include chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and chloroethylene carbonate; Among these, dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and diethyl carbonate are preferable. A carbonate type solvent may be used independently and may be used in mixture of 2 or more types. In the present invention, the cyclic carbonate having an unsaturated bond described later is not included in the carbonate solvent.

1-4. Electrolyte The nonaqueous electrolytic solution of the present invention may contain, as an electrolyte, a compound different from the boron salt compound (2) and / or the boron compound (3) and the imide-based compound (1). As the electrolyte, general formula (4): M′PF _a (C _m F _{2m + 1} ) _6-a (in formula (4), 0 ≦ a ≦ 6, 1 ≦ m ≦ 2,
M ′ represents an alkali metal ion. Hereinafter, it is referred to as an electrolyte (4). It is preferable that it is at least 1 type of compound represented by this.

  In the formula (4), examples of the alkali metal ion represented by M ′ include lithium ion, sodium ion, potassium ion, rubidium ion, and cesium ion. Lithium ions, sodium ions, and potassium ions are preferable, and lithium ions are more preferable.

  When the electrolyte (4) is used in combination, the stability of the non-aqueous electrolyte, the ionic conductivity, and the mobility of the non-aqueous electrolyte are higher than when the imide compound (1) is used alone. It is preferable because it is enhanced.

As the electrolyte (4), LiPF ₆ , LiPF ₃ (CF ₂ CF ₃ ) ₃ , KPF ₆ , KPF ₃ (
CF ₂ CF ₃ ) ₃ is preferable, among which LiPF ₆ and LiPF ₃ (CF ₂ CF ₃ ) ₃ are more preferable, and LiPF ₆ is more preferable.

In addition, electrolyte (4) may be used individually by 1 type, and may be used in combination of 2 or more types of electrolyte (4). As a preferable combination when two or more kinds of electrolytes (4) are used, for example, a combination of LiPF ₆ and LiPF ₃ (CF ₂ CF ₃ ) ₃ can be mentioned, but the combination is not limited to these exemplified combinations. Absent. As the electrolyte (4), a commercially available product may be used, or a product synthesized by a conventionally known method may be used.

  The amount of the electrolyte (4) used is 0 parts by mass when the total amount of the imide compound (1) and the borate compound (2) and / or boron compound (3) is 100 parts by mass. It is preferable to set it as 95 mass parts, More preferably, it is 0.5 mass part-90 mass parts, More preferably, it is 1 mass part-85 mass parts. If the amount of the electrolyte (4) used is too large, the viscosity of the non-aqueous electrolyte will increase, the conductivity will decrease, and the desired battery performance may not be fully exhibited. On the other hand, the electrolyte (4) When there is too little usage-amount, the effect derived from electrolyte (4) may be hard to be acquired enough.

In addition, it is preferable that the density | concentration of the electrolyte (4) in the non-aqueous electrolyte of this invention is 0 mol / L-2.0 mol / L. More preferably, it is 0.01 mol / L-1.8 mol / L, More preferably, it is 0.02 mol / L-1.5 mol / L.

1-5. Other Solvent The nonaqueous electrolytic solution of the present invention may contain a solvent other than the carbonate solvent. As the other solvent, any conventionally known non-aqueous solvent used for the non-aqueous electrolyte can be used. For example, ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane; Non-aqueous solvents such as lactones such as -butyrolactone, γ-valerolactone, α-methyl-γ-butyrolactone; chain carboxylic acid esters such as methyl propionate and methyl butyrate; In addition, the said non-aqueous solvent may be used independently and may mix and use 2 or more types.

Among these other solvents, γ-butyrolactone is preferable as a solvent used in combination with a carbonate-based solvent because it can be mixed with a carbonate-based solvent in an arbitrary ratio and has a relatively high dielectric constant.

The other solvent has a blending ratio of the carbonate-based solvent and the other solvent of 99.99: 0.01-0.
. It is preferably used in the range of 01: 99.99 (carbonate: other solvent), more preferably 99.9: 0.1 to 0.1: 99.9, and even more preferably 99: 1 to 1. : 99.

1-6. Additive The non-aqueous electrolyte of the present invention may contain components other than the borate compound (2) and / or the boron compound (3), the imide-based compound, the electrolyte (4), and the solvent. An additive used for improving characteristics and safety may be included.

  As additives, cyclic carbonates having unsaturated bonds such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), methyl vinylene carbonate (MVC), ethyl vinylene carbonate (EVC); fluoroethylene carbonate, trifluoropropylene carbonate, Carbonate compounds such as phenylethylene carbonate and erythritan carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetra Carboxylic anhydrides such as carboxylic dianhydride and phenyl succinic anhydride; ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methane sulfone Sulfur-containing compounds such as methyl, busulfan, sulfolane, sulfolene, dimethyl sulfone, tetramethylthiuram monosulfide; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3- Nitrogen-containing compounds such as dimethyl-2-imidazolidinone and N-methylsuccinimide; phosphates such as monofluorophosphate and difluorophosphate; hydrocarbon compounds such as heptane, octane and cycloheptane It is done.

  The additive is preferably used in a concentration range of 0.1% by mass to 10% by mass in the non-aqueous electrolyte of the present invention (more preferably 0.2% by mass to 8% by mass, and even more preferably 0%). .3 mass% to 5 mass%). When the amount of the additive used is too small, it may be difficult to obtain an effect derived from the additive.On the other hand, even if another additive is used in a large amount, it is difficult to obtain an effect commensurate with the added amount. There is a possibility that the viscosity of the non-aqueous electrolyte increases and the conductivity decreases.

2. Lithium secondary battery The lithium secondary battery of the present invention is characterized in that it comprises a positive electrode and a negative electrode, and has the non-aqueous electrolyte of the present invention as an electrolyte. More specifically, a separator is provided between the positive electrode and the negative electrode, and the nonaqueous electrolytic solution of the present invention is housed in an outer case together with the positive electrode, the negative electrode, and the like while being impregnated in the separator. Has been.

  The shape of the lithium secondary battery according to the present invention is not particularly limited, and any conventionally known shape can be used as the shape of the lithium secondary battery, such as a cylindrical shape, a square shape, a laminate shape, a coin shape, and a large size. . Further, when used as a high voltage power source (several tens of volts to several hundreds of volts) for mounting on an electric vehicle, a hybrid electric vehicle or the like, a battery module configured by connecting individual batteries in series can also be used. .

  The non-aqueous electrolyte of the present invention hardly corrodes the positive electrode current collector even when an imide-based compound is used as an electrolyte. Therefore, the use of the non-aqueous electrolyte hardly causes deterioration of battery performance over time. A lithium secondary battery can be provided.

2-1. The positive electrode is a positive electrode active material composition containing a positive electrode active material, a conductive additive, a binder, a dispersion solvent and the like supported on a positive electrode current collector, and is usually formed into a sheet shape. .

  As a method for producing the positive electrode, for example, a method in which the positive electrode active material composition is applied to the positive electrode current collector by the doctor blade method or the like and dried after being immersed; the positive electrode active material composition is kneaded and dried. A method in which the obtained sheet is bonded to the positive electrode current collector via a conductive adhesive, pressed, and dried; a positive electrode active material composition to which a liquid lubricant is added is applied or cast on the positive electrode current collector; Examples include a method in which after forming into a desired shape, the liquid lubricant is removed, and then the film is stretched in a uniaxial or multiaxial direction.

2-1-1. Positive electrode current collector The material of the positive electrode current collector is not particularly limited, and for example, conductive metals such as aluminum, aluminum alloy, SUS (stainless steel), and titanium can be used. Among these, aluminum is preferable because it is easy to process into a thin film and is inexpensive. Moreover, the corrosion inhibitory effect of this invention is effectively acquired when aluminum is used as a positive electrode current collector.

2-1-2. Positive Electrode Active Material As the positive electrode active material, any known positive electrode active material used in lithium secondary batteries may be used as long as it can occlude and release lithium ions.

Specifically, lithium cobalt acid, lithium nickel acid, lithium manganese _{acid, LiNi 1-xy Co x Mn} y O 2 or _{LiNi 1-xy Co x Al y} O 2 (0 ≦ x ≦ 1,0 ≦ y ≦ 1 ) Transition metal oxides such as ternary oxides, compounds having an olivine structure such as LiAPO ₄ (A = Fe, Mn, Ni, Co), and solid solution materials incorporating a plurality of transition metals (electrochemistry) Inactive layered Li ₂ MnO ₃ and electrochemically active layered LiM ″ O [M ″ = transition metal such as Co and Ni]) can be exemplified as the positive electrode active material. . These positive electrode active materials may be used individually by 1 type, or may be used in combination of multiple.

2-1-3. Conductive aid Examples of the conductive aid include acetylene black, carbon black, graphite, metal powder material, single-walled carbon nanotube, multi-walled carbon nanotube, and vapor grown carbon fiber.

2-1-4. Binders As binders, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene; synthetic rubbers such as styrene-butadiene rubber and nitrile butadiene rubber; polyamide resins such as polyamideimide; polyethylene, polypropylene and the like Polyolefin resin; poly (meth) acrylic resin; polyacrylic acid; cellulose resin such as carboxymethylcellulose; These binders may be used alone or in combination of two or more. These binders may be dissolved in a solvent at the time of use or dispersed in a solvent.

  The blending amounts of the conductive auxiliary agent and the binder can be appropriately adjusted in consideration of the intended use of the battery (emphasis on output, importance on energy, etc.), ion conductivity, and the like.

In producing the positive electrode, examples of the solvent used in the positive electrode active material composition include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetone, ethanol, ethyl acetate, and water. These solvents may be used in combination. The amount of the solvent used is not particularly limited, and may be appropriately determined according to the production method and the material to be used.

2-2. Negative electrode A negative electrode is a negative electrode active material composition containing a negative electrode active material, a dispersing solvent, a binder and, if necessary, a conductive additive, etc. supported on a negative electrode current collector. Molded.

2-2-1. Negative Electrode Current Collector As a material for the negative electrode current collector, a conductive metal such as copper, iron, nickel, silver, stainless steel (SUS) can be used. From the viewpoint of easy processing into a thin film, copper is preferable.

2-2-2. Negative electrode active material As the negative electrode active material, a conventionally known negative electrode active material used in lithium secondary batteries can be used as long as it can occlude and release lithium ions. Specifically, graphite materials such as artificial graphite and natural graphite, mesophase fired bodies made from coal / petroleum pitch, carbon materials such as non-graphitizable carbon, Si, Si alloys, Si-based negative electrode materials such as SiO, Sn An Sn-based negative electrode material such as an alloy, or a lithium alloy such as lithium metal or a lithium-aluminum alloy can be used.

  As a manufacturing method of the negative electrode, a method similar to the manufacturing method of the positive electrode can be employed. In addition, the same conductive auxiliary agent, binder, and material dispersing solvent as used in the positive electrode are used in the production of the negative electrode.

2-3. Separator The separator is disposed so as to separate the positive electrode and the negative electrode. There is no restriction | limiting in particular in a separator, In this invention, all the conventionally well-known separators can be used. Specific examples of the separator include a porous sheet made of a polymer that absorbs and retains a nonaqueous electrolytic solution (for example, a polyolefin microporous separator or a cellulose separator), a nonwoven fabric separator, a porous metal body, and the like. It is done. Among these, a polyolefin-based microporous separator is preferable because it has a property of being chemically stable to an organic solvent.

  Examples of the material for the porous sheet include polyethylene, polypropylene, and a laminate having a three-layer structure of polypropylene / polyethylene / polypropylene.

  Examples of the material of the nonwoven fabric separator include cotton, rayon, acetate, nylon, polyester, polypropylene, polyethylene, polyimide, aramid, glass, etc., depending on the mechanical strength required for the non-aqueous electrolyte layer, etc. The above-exemplified materials can be used alone or in combination.

2-4. Battery exterior material A battery element provided with a positive electrode, a negative electrode, a separator, the nonaqueous electrolyte of the present invention, etc. is accommodated in a battery exterior material to protect the battery element from external impact, environmental degradation, etc. when the battery is used. . In the present invention, the material of the battery exterior material is not particularly limited, and any conventionally known exterior material can be used.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Example 1
Lithium bis (fluorosulfonyl) imide (LiFSI) in a non-aqueous solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at 3: 7 (volume ratio) so that the concentration becomes 1.0 mol / L. , Made by Nippon Shokubai Co., Ltd., an imide-based alkali metal salt (1)) was dissolved. Next, 0.12 g of LiBF ₄ (manufactured by Kishida Chemical Co., Ltd.) is added to 6 g of this solution so that the concentration in the solution is 1% by mass, and a non-aqueous electrolyte (1
) Was prepared.

[Cyclic voltammetry (CV measurement)]
Cyclic voltammetry was performed in a 25 ° C. atmosphere using a three-electrode cell and an electrochemical measurement device (“HSV-100”, manufactured by Hokuto Denko Corporation). Aluminum foil (1085 material, manufactured by Nippon Foil Co., Ltd.) was used for the working electrode in the three-electrode cell, and lithium metal (manufactured by Honjo Metal Co., Ltd.) was used for the reference electrode and the counter electrode.

The measurement was performed between 2.4 V and 5 V (vs. Li / Li ⁺ ) using a non-aqueous electrolyte (1) as the electrolyte and a sweep rate of 10 mV / s. The results are shown in FIG.

[Constant voltage application test]
The constant voltage application test was performed in a 25 ° C. atmosphere using a three-electrode cell and an electrochemical measurement device (“HZ-5000”, manufactured by Hokuto Denko Corporation). Aluminum foil (1085 material, manufactured by Nippon Foil Co., Ltd.) was used for the working electrode in the three-electrode cell, and lithium metal (manufactured by Honjo Metal Co., Ltd.) was used for the reference electrode and the counter electrode.

In the test, the CV measurement using the non-aqueous electrolyte (1) as an electrolyte was performed, and then the applied voltage was set to 4.4V, 4.6V, 4.8V, and 5.0V. Record the current value when a constant voltage is applied, and evaluate that the current value after 2 hours from the start of the test is less than 1.0 × 10 ⁻³ mA / cm ² as “◯” (no corrosion occurred) It evaluated as "x" (corrosion generation | occurrence | production) of 1.0 * 10 < ^-3 > mA / cm < ² > or more.

[Surface observation]
The aluminum foil (working electrode) after the constant voltage application test was observed with a digital microscope (magnification: 1000 times, field of view: 3 mm × 3 mm, manufactured by Keyence Corporation) to confirm the presence or absence of pitting corrosion due to corrosion. The case where pitting corrosion was observed on the aluminum foil was evaluated as “×”, and the case where pitting corrosion was not observed was evaluated as “◯”. The results are shown in Table 1.

Comparative Example 1
A nonaqueous electrolytic solution (2) was prepared in the same manner as in Example 1 except that LiPF ₆ was used instead of LiBF ₄ , and CV measurement and constant voltage application test were performed. The results are shown in Table 1 and FIG.

As shown in FIG. 1, in Example 1 using the non-aqueous electrolyte (1) containing LiBF ₄ , a large current flowed in the first cycle, but the current density decreased in the second and subsequent cycles. From this, it is suggested that more current flows for the generation of the passive film in the first cycle, and that the corrosion is suppressed by the generated passive film in the second and subsequent cycles. Furthermore, even if the number of cycles was repeated, the increase in the current value was suppressed.

In contrast, a non-aqueous electrolyte (2) using LiPF ₆ instead of the borate compound (2)
In the case of Comparative Example 1 using No. 1, as shown in FIG. 2, corrosion behavior was observed in the first cycle. In addition, hysteresis was observed in the second and third cycles, and this result suggested that fine corrosion occurred in the working electrode, and pitting corrosion was actually confirmed by surface observation (Table 1). ).

From Table 1, in Example 1, even at an applied voltage of 5.0 V, the current value was less than 1.0 × 10 ⁻³ mA / cm ² , and no pitting corrosion was observed on the surface of the aluminum foil in surface observation. .
This is in good agreement with the CV measurement result suggesting that a passive film was formed on the surface of the aluminum foil (working electrode). On the other hand, in Comparative Example 1, the current value already exceeded 1.0 × 10 ⁻³ mA / cm ² when the applied voltage was 4.4 V, and pitting corrosion due to corrosion was also confirmed in the surface observation.

From these results, in the non-aqueous electrolyte containing the imide-based compound (1), the borate compound (2) and / or the boron compound (3) is an essential component of the non-aqueous electrolyte so It can be seen that a conductor film can be formed and corrosion of the aluminum current collector can be suppressed more effectively than when LiPF ₆ is used.

Claims (8)

An imide compound represented by the following general formula (1);
(XSO ₂ ) (X′SO ₂ ) N ⁻ Li ⁺ (1)
(X and X ′ represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group having 1 to 6 carbon atoms, and at least one of X and X ′ is a fluorine atom.)
A borate compound represented by the following general formula (2) and / or a boron compound represented by the following general formula (3);
_{^{M n + [(BY 1 4}} ) -] n (2)
BY ² ₃ (3)
(In the formulas (2) and (3), M ^{n +} represents a monovalent, divalent, or trivalent organic or inorganic cation, and Y ¹ and Y ² are the same or different and represent a hydrogen atom, a halogen atom, or a cyano group. Represents a hydrocarbon group having 1 to 10 carbon atoms in the main chain optionally having halogen, -Z ¹ R ¹⁴ , wherein R ¹⁴ is a hydrogen atom, a halogen atom, or a main chain having 1 to 4 atoms; 10 represents an organic substituent, Z ¹ represents O or S, and n represents an integer of 1 to 3.)
A nonaqueous electrolytic solution comprising a carbonate-based solvent.   The non-aqueous electrolyte of Claim 1 containing the borate compound represented by the said General formula (2). The nonaqueous electrolytic solution according to claim ¹ , wherein Y ¹ is a fluorine atom or a fluoroalkyl group in the borate compound represented by the general formula (2).   The nonaqueous electrolytic solution according to any one of claims 1 to 3, wherein the borate compound represented by the general formula (2) includes a boron tetrafluoride anion. Furthermore, the non-aqueous electrolyte in any one of Claims 1-4 containing the electrolyte represented by following General formula (4).
M′PF _a (C _m F _{2m + 1} ) _6-a (0 ≦ a ≦ 6, 1 ≦ m ≦ 2) (4)
(In formula (4), M ′ represents an alkali metal ion.)   The non-aqueous electrolyte according to claim 1, wherein the imide compound represented by the general formula (1) is lithium bis (fluorosulfonyl) imide. The nonaqueous electrolytic solution according to claim 5 or 6, wherein the electrolyte represented by the formula (4) is LiPF ₆ .   A lithium secondary battery using the nonaqueous electrolytic solution according to claim 1.